Q. Two point sources distance 0.1 meter away viewed by a telescope. The objective is covered by a screen having a hole of 1mm width. If the wavelength of the light used is 6500Å, then the maximum distance at which the two sources are seen just resolved, will be nearly
(a) 125.0 m
(b) 164 m
(c) 131 m
(d) 144 m
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Ans: (a)
Sol: Resolving Power = 1/Δθ = D/1.22λ
=> Δθ = 1.22λ/D
As , Δθ = x/d
Hence x/d = 1.22λ/D
=> d= xD/1.22λ
= 0.1×1×10−3/1.22×6500
= 125 m